Blender Hand Twisting
It seems normal that if you rotate the hand, the wrist mesh get twisted too. What you should do is make the forearm rotate as well so that the torsion looks more natural.
To do so you need to give your forearm bone a Copy Rotation constraint, with the left hand as Target and Space &gt; Pose Space /Pose Space. The problem is that for the moment it will mess up because the forearm can’t be both the parent of the hand and be affected by the rotation of the hand.
So what you should do is:

Create a bone under the wrist, it will be the controller bone, parent it to the armature root bone (in Keep Offset mode).
Parent the hand to the controller (in Keep Offset mode).
Give the forearm a second constraint, the Inverse Kinematic constraint, with the controller as target, and a Chain Length of 2 (it controls the fore arm and the upper arm).

Now when you rotate the controller, it makes the hand rotate, and it makes the forearm move and rotate as well.
Also maybe in Edit mode, pull the elbow a bit downards so that the arm bend a bit, and create a bone (parented to the root as well) that you put behind the elbow to create the Inverse Kinematic Pole Target.